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doi:10.2204/iodp.proc.301.106.2005

Operations

This section describes the sequence of drilling, coring, and engineering operations conducted during Expedition 301 at Site U1301. Operations at Site 1026 are described in "Operations" in the "Site 1026" chapter. Expedition 301 operations are summarized in Table T1 in the "Expedition 301 summary" chapter.

Astoria, Oregon, port call

After the 17 day transit across the Pacific Ocean, the ship arrived in Astoria, Oregon (USA), ~1.5 days ahead of schedule at 1600 h on 18 June 2004. All times presented in this report are local ship time, which was Universal Time Coordinated – 7 h. The Astoria port call leading up to Expedition 301 was extensive because of the activities required to remobilize the JOIDES Resolution for IODP operations as well as loading all of the special hardware required for Expedition 301. The mobilization actually began long before Astoria with the official acceptance of the drillship JOIDES Resolution on 31 May in Gamagori, Japan. In Japan we (1) loaded laboratory equipment and supplies required to bring the shipboard laboratories back up to operational status, (2) loaded some bits and bottom-hole assembly (BHA) subs, and (3) had the active heave compensator serviced.

In Astoria, ~40 truckloads of materials required for remobilization and Expedition 301 were delivered. Items loaded included drill pipe, all bulk materials (mud and cement), casing, all remaining operations drilling equipment, a new heave-compensated logging line/winch, laboratory equipment and supplies, and most of the specialty hole completion equipment required for replacing two existing CORKs and installing two new CORK systems.

The Astoria port call was scheduled for 8 days but was completed in just over 7 days. The Expedition 301 portion of the Astoria port call officially began at 0600 h on 27 June. Because of the early ship arrival, excellent weather, and exceptionally efficient loading activities and coordination, the ship was ready to depart Astoria only 1 h after the "official" Expedition 301 port call began. Once the oncoming captain was satisfied with the ship's readiness for sea and the last of the expedition hardware was loaded, the ship was deemed ready to depart Astoria for the first site.

Site U1301

Transit to Site U1301 (proposed Site SR-1A)

All major operations conducted during Expedition 301 are listed in Table T1 in the "Expedition 301 summary" chapter. The last line away from Pier 1 took place at 0833 h on 27 June 2004. The forward and aft tugs were released, and the JOIDES Resolution proceeded down the Columbia River and across the Columbia Bar. The pilot departed the ship via helicopter, and at 1030 h, the vessel was under way at full speed on a course of 302° for Site U1301 (SR-1A). The transit was quick and uneventful, 172 nmi in 16.6 h at an average speed of 10.4 kt. After reducing speed upon approach to the site, the thrusters and hydrophones were lowered and the vessel switched to dynamic positioning (DP) control at 0321 h on 28 June.

Hole U1301A

Arrival on site and jet-in test

The DP operator positioned the ship over the Global Positioning System coordinates for Site U1301, and a Datasonics model 354M, 15 KHz, 208 Db beacon (SN 2202) was deployed at 0722 h on 28 June 2004. For the jet-in test only, we offset the ship 10 m north and 10 m west from the primary site coordinates. Operations in Hole 1301A are summarized in Table T1 in the "Expedition 301 summary" chapter and Table T1, and final formation and casing depths are given in Table T2.

The initial operation was to move the previously assembled reentry cone off of the moonpool doors, lay out the upper guide horn, and pick up eight drill collars from the forward pipe rack. The BHA and other drill string components were strapped (measured) and drifted (through bore clearance check) as they were made up and lowered through the rig floor. The camera/sonar system was deployed, and the bit was observed tagging the seafloor at 2667.5 meters below rig floor (mbrf) as measured from the dual elevator stool. This depth was later adjusted to 2667.3 mbrf.

A jet-in test to verify how much 20 inch casing could be washed beneath the reentry cone was initiated using an 18½ inch tricone drill bit fitted with three number 16 jets. The jet-in test required more strokes per minute with the rig circulating pumps and higher weight on bit (WOB) than was required for the Leg 168 jet-in test conducted for Hole 1026B located ~1 nmi away. The jet-in test was terminated after 5.75 h at 41.4 mbsf. After recovering the jet-in assembly, we discovered that one of the bit jets was plugged. This may partially explain the higher pump pressures and slower jetting process; however, we decided to reduce the length of 20 inch casing from ~75 to ~39 m.

Deployment of reentry cone and 20 inch casing

We painted the reentry cone for Hole U1301A with a black rim around the top of the cone and one internal panel painted black with white lettering that reads "1301A" (Fig. F4). The opposite panel was left gray but lettered with white lettering that reads "1301A." We also painted a black ring internally halfway down the cone. On the outside there were two opposing panels painted with white numbers that read "1301A."

After moving the reentry cone back over center in the moonpool, the rig floor was prepared for running 20 inch casing. This casing assembly consisted of a shoe joint cut to the appropriate length and welded out to a standard 20 inch Texas pattern casing shoe, two joints of 20 inch casing (94 lb/ft; K-55; range-3; buttress thread), a standard 20 inch casing pup joint, and a 20 inch Dril-Quip (DQ) casing hanger. The hanger was latched into the reentry cone bore, and latch ring engagement was verified by visually observing that the latch ring was in the appropriate position as viewed through the disengagement holes. Because the typical "audible" latch ring engagement snapping sound was not heard, the hanger was tack-welded in four places in the casing hanger flutes. This was done to avoid inadvertent disengagement during the trip to the seafloor. After assembling the BHA, the DQ casing running tool was made up to the 20 inch casing hanger and the entire assembly was ready for lowering. At 1600 h on 29 June, Hole U1301A was spudded as the 20 inch casing shoe tagged the seafloor. Jetting of the 20 inch conductor casing proceeded well, and 7 h later we landed and released the reentry cone base at the seafloor. The DQ running tool was released at 2300 h, and the drill string was tripped back to the surface.

Drilling 20 inch hole in sediment for 16 inch casing

The first change to the initial operations plan for this site came with the drilling of the hole for the 16 inch casing string. The original plan called for drilling a nominal 21½ inch diameter hole using a bicentered reamer (Downhole Design, Inc. [DDI]; B182X215). This tool was used successfully during ODP Leg 206 to drill two basement holes. In talking with members of the drill crew and the ODP Operations Superintendent for that leg, we learned that the tool did not perform as intended. They were able to drill successfully in basement rock; however, the 9⅞ inch tricone bit used as a pilot for the bicentered reamer assembly catastrophically failed twice, leaving bit cones in the hole. This was attributed to lateral loading of the bit during the bicenter functioning of the reamer head. For our expedition, DDI provided a 9⅞ inch stabilizer sub to run directly above the pilot bit. In addition, a specially designed 9⅞ inch pilot "wobble" bit was provided to replace the conventional 9⅞ inch tricone bit. The Leg 206 crew also indicated that the bicenter reamer did not drill a very good hole in the softer sediments overlying the hard basement rock. It was believed that this may have contributed to problems emplacing the 16 inch casing strings during Leg 206. With this added knowledge, we modified the operations plan for Expedition 301. We decided to deploy a more conventional "arm-style" underreamer to drill the sediment section of the hole, to be followed, after a drill string round trip, with the bicenter reamer assembly to drill the upper ~15 m of basement. We decided to accept the extra time for another pipe trip in order to avoid both the problems experienced during Leg 206 and having to drill with the conventional arm-style underreamer in basement rock, which historically has had integrity problems that led to underreamer failure.

A Hole Opener Company (HOC) model DTU 1175 underreamer outfitted with three number 12 jets was made up with the same 18½ inch tricone bit (fitted with three number 16 jets) and used in jetting-in the 20 inch casing and reentry cone. The underreamer was function-tested in the moonpool by pumping with a circulating head and visually observing and measuring the opening or extension diameter of the underreamer arms at 20 inches. This underreamer had recently been refurbished on shore, and the function test was successfully completed by 1230 h on 30 June.

The drilling assembly was lowered, the camera/sonar system was deployed, and Hole U1301A was reentered for the first time after <5 min. Once inside the 20 inch casing the top drive was picked up, the camera was recovered, and drilling commenced at 1530 h. After an initial slow advance of 6 m directly below the 20 inch casing shoe (to keep from opening the underreamer arms inside the casing), the underreamer was opened up and drilling continued to 262.2 mbsf. An abrupt change in rate of penetration (ROP), coupled with the typical "basalt bounce" associated with hard rock drilling, was a clear indication that we had reached our basement target, originally projected to be at ~275 mbsf. Overall net ROP (including connection time) with the conventional underreamer in sediment was 16.5 m/h. Actual drilling ROP was 22.3 m/h. Control drilling techniques were employed to ensure that a good quality hole was obtained.

The hole was swept with 50 bbl of sepiolite drilling mud. The drill string was recovered, and the underreamer and pilot bit were laid out by 1130 h on 1 July.

Drilling 21½ inch hole in basement for 16 inch casing

A DDI bicenter reamer (BCR; B182X215) assembly, including a 9⅞ inch stabilizer and a 9⅞ inch pilot wobble bit, was made up to the BHA and lowered to the seafloor. This BCR configuration is designed to drill a 21½ inch diameter hole yet be able to pass through a diameter of 18¼ inch—this would allow it to safely pass through the 20 inch casing string, which has a nominal internal diameter (ID) of 19⅛ inch. After another 5 min reentry, the drilling assembly was lowered to 233.7 mbsf without incident. The top drive was picked up, and the pipe was lowered the remaining distance to the bottom of the hole. At 1900 h on 1 July, basement drilling with the BCR commenced. Drilling proceeded well at first, with 7.3 m of advance drilled at an average ROP of 1.5 m/h. The last 1.8 m only drilled at 0.6 m/h, and, after sweeping the hole with 50 bbl of sepiolite mud, a wiper trip back above the basement contact at 262.2 mbsf was made. Two more wiper trips were made through this interval, interspersed with two more 50 bbl sepiolite mud sweeps. The lowermost 2–4 m of hole never did clean up adequately, and it was felt that attempting to advance the hole further with this drilling assembly was not prudent and risked tool failure. Significantly elevated drilling torque, >450 A rather than the earlier 150 A, led us to abandon further attempts at deepening the hole with the BCR assembly, and we elected to recover the drill string short of our original target depth of 272–276 mbsf. The hole was displaced with sepiolite mud, and the drill string was recovered on the rig floor at 1400 h on 2 July.

Deploying and cementing 16 inch casing

The subsea release (SSR) plug assembly was made up to the DQ casing running tool and secured in the derrick. After conducting a safety meeting, preparations were made for running 16 inch casing. The shoe joint was picked up, and the cementing float shoe was attached to the lowermost joint of 16 inch casing. Another 19 joints of standard 16 inch (75 lb/ft buttress) casing were made up, and the 16 inch casing hanger was attached to the top of the string. The casing running tool was engaged with the 16 inch casing hanger, and the string was lowered to 2643 mbrf and spaced out for reentry. Another quick reentry (10 min) was made into Hole U1301A at 0045 h on 3 July. The casing string was lowered without resistance to 2902 mbrf (234.3 mbsf), where the top drive was picked up. We continued washing down the casing to 2924 mbrf (256.3 mbsf), and the cementing manifold was picked up. The 16 inch hanger was landed and latch-in was verified at 0315 h. The cementing operation proceeded smoothly, with 18 bbl of 15.8 lb per gallon (ppg) cement mixed up and displaced downhole. The cementing dart landed at the proper amount of strokes (~1220) indicated by a standpipe pressure rise to 2600 psi. The SSR dart/wiper plug assembly also landed at the proper amount of strokes (~1600), and a pressure of 500 psi was maintained. After releasing the pressure at the standpipe, a check was made to confirm that no flowback was occurring. The cementing swivel hose was disconnected, and, after 3¼ turns to the right, the casing running tool was released. The end of the drill string was pulled clear of the reentry cone and secured for a routine servicing of the drill line (slip and cut) prior to retrieving the drill string. By 1230 h, the drill string was back on the rig floor. The casing running tool was detorqued and laid out with the SSR assembly.

Drilling 14¾ inch hole in basement for 10¾ inch casing

A new 14½ inch tricone drill bit (Varel type ETD617) was made up, and six 8¼ inch drill collars were picked up from the forward tubular rack. A five-stand drilling BHA was assembled, which allowed us to drill 130 m past the 16 inch casing shoe without placing the tapered drill collar (TDC) in open hole. Therefore, the drilling assembly exposed to open hole would consist entirely of slickwall pipe (8¼ inch drill collars) all the way down to the top of the 14¾ inch tricone drill bit.

The drill string was lowered to 2658.9 mbrf, stopping to fill the pipe every 30 stands. After spacing out the drill string, another 5 min reentry was made into the Hole U1301A. After retrieving the camera system, the pipe was lowered an additional four stands and the top drive was picked up in preparation for drilling. At 2130 h on 3 July, the top of the 16 inch wiper plug was contacted and we commenced drilling out the wiper plug, dart, and float shoe assembly. Once through the shoe, the hole cleaning continued to 270.3 mbsf (1.0 m off bottom), when the bit was 8.1 m into basement. Drilling operations then continued with the drilling of the 14¾ inch diameter hole for the 10¾ inch casing string.

At 0015 h on 5 July, we terminated drilling the 14¾ inch hole at 3037.0 mbrf (369.7 mbsf). This was 107.5 m into basement. The upper ~42 m of basement drilled at 3.0–3.5 m/h. At ~304 mbsf, the ROP began to steadily increase to ~8.0 m/h, and this continued to ~357 mbsf. Only a few relatively thin spots (<0.5 m) of 4 m/h drilling rates were interspersed through this interval (see Fig. F9 in the "Expedition 301 summary" chapter). The zones of rapid penetration concerned us, and those fears proved to be well founded. The next 20+ h were spent fighting hole problems. Multiple wiper trips, reaming operations, mud sweeps, and so on were required before the hole eventually cleaned up to what we considered reasonable for attempting to emplace casing. The hole was displaced with sepiolite mud, and at 2000 h on 5 July we made one final pipe trip up inside the 16 inch casing hanger at 259.3 mbsf. We then lowered the bit back into open hole without rotation or circulation. The bit reached 3016 mbrf (348.3 mbsf) before taking 20,000 lb weight. The driller then broke circulation and proceeded to wash down to bottom. The hole was swept one final time with 50 bbl of sepiolite and then displaced with sepiolite mud. The drill string was recovered on board by 0400 h on 6 July.

First attempt at deploying 10¾ inch casing

Twenty-seven joints of 10½ inch casing (40.5 lb/ft; K-55; range 3; buttress thread) were made up with a standard Halliburton cementing float shoe on the bottom and a conventional DQ 10¾ inch casing hanger/pup joint at the top. After attaching the casing running tool, the casing assembly was lowered to the seafloor. Once the camera system could see the bottom, we reentered Hole U1301A with the casing string within 5 min (at 1415 h). Problems ensued almost immediately. The 10¾ inch casing shoe encountered resistance ~4 m below the 16 inch casing shoe (~3 m into basement). The casing was worked past this ledge, and by 2030 h we had managed to work the 10¾ inch casing to 355.6 mbsf, or 93.2 m into basement. This was just 4.5 m shy of our hanger landing depth. With confidence mounting, we shut down circulation and picked up the cementing manifold and swivel assembly. Once operations resumed (~16 min later), we found that we were unable to move the casing down any further. The hole appeared to be collapsing in above us, although we still were able to maintain unrestricted circulation. We could not pass 3023.3 mbrf (355.6 mbsf), and we also had problems pulling back uphole (20,000–40,000 lb overpull). The casing could be pulled back up with overpull but would not go back down. After pulling the casing shoe back to 309.3 mbsf (46.9 m into basement), all drilling parameters returned to normal. Speculation was that rocks fell in from above and would only allow movement in the upward direction. Once this material was below us, the casing was once again free to move up or down freely. By 2400 h on 6 July, the casing had been once again lowered to 3010.8 mbrf (343.1 mbsf). At this point, the upper hole problems again prevented us from advancing any further. At 0400 h on 7 July, we stopped attempting to land the casing and decided instead to recover the casing string, shorten it up considerably, and make Hole U1301A an installation to monitor uppermost basement.

After pulling the casing string back to the ship, we laid out the casing hanger and then began to lay out the first of what was supposed to be a total of seven joints of 10¾ inch casing. The first joint was laid out correctly. The second joint appeared to be slightly bent. The next five joints were noticeably bent, so we continued on and checked the next two joints beyond the original number of joints we intended to take out of the casing string. The sixth joint was also bent, but from that point on the string was all right. All bent joints had been above the seafloor during the attempts at getting past the problem zone.

Second attempt at deploying 10¾ inch casing

A single "replacement" joint of 10¾ inch casing was picked up and made part of the original casing string. All six of the recovered bent joints were marked and stored in the riser hold. The 10¾ inch casing hanger was then made up, the running tool was attached, the remainder of the BHA was assembled, and the 10¾ inch casing string was lowered for the second time. Space out for the new casing string was designed to place the casing shoe into the upper portion of basement above the zone of rapid ROP and fairly close to the sediment/basement interface so as to have the best chance of a good cement seal and limited lateral dispersion of the cement into the formation. We felt that attempting to place the 10¾ inch casing shoe too far into the upper "fractured" basement would risk not getting the cement to reach back up to the 16 inch casing shoe, which was essential for sealing the hole for the CORK hydrologic experiment. The objective of the shallow sampling hole was to sample the "upper" few tens of meters of basement; our planned 10¾ inch casing shoe depth would achieve this, and placing it deeper into the "upper" basement would not improve upon this goal.

The subsequent reentry of Hole U1301A was made more interesting than the previous ones due to a cloud of drilling mud that was suspended in and around the reentry cone, significantly obscuring visibility. Instead of the camera, the sonar system was used primarily to locate the cone and was also a major contributor in helping to make the reentry itself. After 45 min, Hole U1301A was reentered for the sixth time, and the shortened version of the 10¾ inch casing string was lowered into the hole and landed without incident, placing the 10¾ inch casing shoe at 277.1 mbsf, or 14.9 m into basement. Hanger latch engagement was confirmed with 15,000 lb of overpull, and the shoe was cemented in place with 10 bbl of 15.2 ppg class G cement. The cementing operation using the SSR system was completed without incident, and at 0035 h on 8 July the casing running tool was released. The initial phase of operations in Hole U1301A was completed with the recovery of the drill string at 0800 h on 8 July.

We decided to temporarily halt operations in Hole U1301A to allow the cement to set, to allow the hole time to equilibrate, and to initiate operations in Hole U1301B.

Transit to Hole U1301B

Hole U1301B was located only 36 m northeast of Hole U1301A, so the ship was offset in DP mode while the drill crew continued to retrieve the drill string. The scientists wanted to have Hole U1301B as close to Hole U1301A as technically possible for the potential of being able to investigate vertical flow. Because of the close proximity of the holes, a jet-in test was considered unnecessary.

Hole U1301B

Operations in Hole 1301B are summarized in Table T1 in the "Expedition 301 summary" chapter and Table T1, and final formation and casing depths are given in Table T3.

Deployment of reentry cone and 20 inch casing

The reentry cone for Hole U1301B was painted (Fig. F5) so as to readily distinguish it from the Hole U1301A reentry cone. The reentry cone for Hole U1301B had three internally alternating black panels with a black rim on the top of the black panels only; the rims of the nonpainted panels were painted black on the corners only. The center black panel was lettered "1301B" with white lettering. On the outside of the internally lettered panels were letters painted "1301B" in white against a black background.

The newly painted reentry cone was moved over center in the moonpool, and the rig floor was prepared for running 20 inch casing. This assembly consisted of a shoe joint previously cut to the appropriate length and welded out to a standard 20 inch Texas pattern casing shoe, two joints of 20 inch casing (94 lb/ft; K-55; range-3; buttress thread), a standard 20 inch casing pup joint, and a 20 inch DQ casing hanger. The hanger was latched into the reentry cone, and latch ring engagement was verified by visually observing that the latch ring was in the appropriate position as viewed through the disengagement holes. Unlike the previous 20 inch latch-in operation, this time the distinctive "audible snap" was heard as the latch ring engaged. After assembling the BHA, the casing running tool was made up to the 20 inch casing hanger and the entire assembly was ready for lowering. At 2000 h on 8 July 2004, Hole U1301B was spudded as the 20 inch casing shoe tagged the seafloor. Jetting of the 20 inch conductor casing proceeded well, and 6.5 h later we landed and released the reentry cone base at the seafloor. Release of the DQ running tool was again executed perfectly, and by 0900 h on 9 July the drill string was back on board ship.

Drilling 20 inch hole for 16 inch casing

The same Smith 18½ inch Model 2JS tricone drill bit (jetted with one number 16 and two number 24 nozzles) and the same HOC model DTU 1175 underreamer (outfitted with three number 12 jets) were made up and prepared for running in the hole. As is customary, the underreamer was function-tested by pumping with a circulating head to visually observe that the underreamer arms would open correctly. Even with 90 spm and 900 psi pressure, the arms failed to extend. At 1300 h on 9 July, we decided to suspend operations long enough to rebuild the single set of large underreamers that we had on board. Drilling the hole only with the 18½ inch bit was discussed and rejected, as was the use of the 21½ inch BCR (per previous experience discussed earlier). The underreamer was torn down by placing the body vertically in the rotary table. The seals were replaced, and 3.75 h later the tool had been rebuilt and successfully function-tested.

The drilling assembly was lowered to the seafloor, the camera system was deployed, and the drill crew serviced the drill line (slip and cut). Prior to reentry, we lowered the pipe and visually observed the bit tag the seafloor adjacent to the reentry cone. Seafloor depth for Hole U1301B was confirmed to be 1.0 m higher than Hole U1301A at 2666.5 mbrf. This depth was later adjusted to 2667.8 mbrf. Hole U1301B was reentered for the first time in virtually seconds. As the bit was lifted off the seafloor, it swung directly over the reentry cone and the reentry was made at 2245 h on 9 July.

Once inside the 20 inch casing, the top drive was picked up, the camera was recovered, and drilling commenced at 0015 h on 10 July. After an initial slow advance of ~9 m directly below the 20 inch casing shoe (to keep from opening the underreamer arms inside the casing), the underreamer was opened up and drilling continued to 2933.0 mbrf (265.2 mbsf). An abrupt change in ROP at 1015 h, coupled with the typical "basalt bounce" associated with hard rock drilling, was a clear indication that we had reached our basement target 4.1 m shallower than we did in Hole U1301A. The underreamer, with arm extension set at 20 inches, was installed ~8 m above the bit. The 18½ inch tricone bit with the 20 inch underreamer above drilled the sediment at an average rate of 35.0 m/h. The average "net" ROP in sediment was ~23 m/h (including connection time). We continued drilling in basement to 2943.0 mbrf (275.2 mbsf). The ROP for the 18½ inch bit in basement (first 8 m) was 3.6 m/h using a WOB of ~15,000 lb. An additional 2 m of basement was then drilled with the underreamer penetrating the top of basement, placing the depth of the 20 inch hole at 2935.0 mbrf (267.2 mbsf). The actual ROP for the 2 m of basement drilled with the 20 inch underreamer was ~1.3 m/h using a reduced WOB of 10,000–12,000 lb. Other notable drilling parameters were rotation = 60–70 rpm, two pumps at 80 spm each, and pump pressure = 1450–1475 psi.

We then raised the bit to 2910.0 mbrf (242.2 mbsf), set back the top drive, and continued up to 2707.0 mbrf (39.2 mbsf). While lowering back into the hole, we began to take weight at 2906.0 mbrf (238.2 mbsf). The top drive was picked up, and we continued to wash and ream the hole at 2906.0 mbrf (238.2 mbsf) and from 2910.0 mbrf (241.2 mbsf) to 2943.0 mbrf (275.2 mbsf). There was no fill encountered at TD.

We swept the hole with 50 bbl of sepiolite mud and then made another wiper trip to 2900.0 mbrf (232.2 mbsf) and back to TD. We checked the hole condition at that point by lowering the drilling assembly without pump or rotation until encountering a ledge at 2935.0 mbrf (267.2 mbsf). This was <1.0 m below our target depth for the 16 inch casing shoe of 267.5 mbsf and was considered too close for comfort. We therefore elected to drill an additional 1.0 m of hole into basement. With the 18½ inch hole depth now at 2944.0 mbrf (276.2 mbsf) and the 20 inch hole depth at 2936.0 mbrf (268.2 mbsf), we again swept the hole with 50 bbl of sepiolite mud and proceeded to conduct one last hole inspection to 2900.0 mbrf (232.2 mbsf) and back to TD without rotation or circulation. This time, the hole was deemed in acceptable condition for 16 inch casing deployment.

The hole was swept a final time with 50 bbl of sepiolite mud and then displaced with another 304 bbl of sepiolite prior to retrieving the drill string. When the drill string was recovered, the underreamer arms were still in the expanded position. We were unable to retract the arms. The underreamer and drill bit assembly was laid out by 0615 h on 11 July.

Deploying and cementing 16 inch casing

By drilling the upper 3.0 m of basement with the underreamer assembly, we eliminated the need for another drill string round trip to deploy the bicentered bit assembly. Therefore, our attention turned to making up and deploying the 16 inch casing string. A total of 19 joints of 16 inch casing (75 lb/ft; K-55; range 3) were made up with a cementing float shoe on the bottom and a standard 16 inch casing hanger on the top. The special 16 inch seal bore pup joint was not used, however, because of insufficient clearance (0.015 inch per side) with the 10¾ inch seal sub assembly designed to mate with the seal bore hanger.

To enhance our chances of successfully landing the casing hanger, we amended our operating procedures. We made up a single joint of drill pipe to the bottom of the cementing manifold. In this way, we hoped to speed up the process of adding the cementing manifold to the drill string later. It was during this time, with the circulation pumps shut down, that, based on previous experience, we were most vulnerable to packing of the hole annulus and the attendant problems with getting the casing string moving downhole once again.

The casing string was lowered to the seafloor, the camera system was deployed, and Hole U1301B was reentered for the second time at 1620 h on 11 July. After picking up the top drive, the casing was lowered into open hole and the casing hanger landed without incident at 1800 h. Latch engagement was verified with 15,000 lb of overpull. The 16 inch casing shoe was subsequently cemented in place with 18 bbl of 15.2 ppg cement at a 270.9 mbsf. The casing running tool was released with 3¼ turns to the right, and the drill string/cementing manifold were thoroughly flushed with seawater prior to retrieval.

After recovering and detorquing the casing running tool, the underreamer was placed in the rotary table.

Drilling 14¾ inch hole in basement for 10¾ inch casing

At 0130 h on 12 July, we began making up the 14¾ inch tricone drilling assembly. A five-stand BHA was run so that we could keep the top of the 8¼ inch drill collars inside casing and out of open hole. In this way, we minimized our chances of getting stuck while drilling the 14¾ inch diameter hole.

Hole U1301B was reentered for the third time at 0700 h on 12 July, and by 1030 h the float shoe and cement were drilled out and the hole was cleaned up to TD at 2944.0 mbrf (276.2 mbsf). At 1030 h, we began drilling the 14¾ inch hole in basement required for the 10¾ inch casing string.

Basement drilling was conducted using a new Varel 14¾ inch ETD617 tricone drill bit (SN174706) jetted with three number 20 nozzles. The first 50.0 m of basement drilling was achieved in 13.5 h at an average "net" drilling rate (including connection time) of 3.7 m/h. The actual ROP through this section varied from as much as 6.0 to <1.0 m/h (see Fig. F9 in the "Expedition 301 summary" chapter). Drilling was uneventful until reaching 327.2 mbsf. While picking up to make a connection, the driller noted 20,000 lb of overpull and significantly elevated pump pressures. It appeared that the hole had packed off. The driller continued to fight hole problems including loss of rotation, loss of circulation, overpull, and elevated pump pressure for the next >11 h. Finally, at 1130 h on 13 July, the hole appeared to be stabilized and forward progress continued. By 1530 h, the hole had been advanced to the target depth of 3018.0 mbrf (350.2 mbsf), or 85.0 m into basement.

The hole was swept multiple times with sepiolite mud, and we continued to wash and ream the hole until we were comfortable that hole stability was adequate for casing deployment. By 0215 h the morning of 14 July, the bit was back on board ship and preparations for running the 10¾ inch casing string began.

First attempt at installing 10¾ inch casing

Twenty nine joints of 10¾ inch casing (40.5 lb/ft; K-55; range 3) were made up, along with a cementing float shoe and the 10¾ inch casing hanger. Total string length was 342.50 m. The casing running tool was made up and lowered to the seafloor. The camera was deployed, and Hole U1301B was reentered for the fourth time at 1140 h on 14 July. The casing was lowered to 2964.0 mbrf, and the top drive was picked up. The casing was washed to 3002.0 mbrf (334.2 mbsf) without incident. After picking up the cementing manifold, we found we could not pass 3002.0 mbrf. Nearly 7 h were spent attempting to move the casing further downhole, but all efforts were in vain. The string was entirely free above 3000.0 mbrf but could not be moved any further down the hole. At 1930 h, we abandoned our efforts to install the casing, laid out the cementing manifold, and retrieved the casing string. There were no problems or indications of drag or overpull identified while pulling the casing upward through an open hole. By 0530 h on 15 July, the 10¾ inch casing string had been disassembled and stored away in the riser hold.

Reaming of 14¾ inch hole in basement

A 14¾ inch tricone bit and five-stand drilling BHA was assembled and lowered to the seafloor. Reentry number 5 was made into Hole U1301B in short order, and at 1015 h on 15 July we began to lower the bit to 2965.0 mbrf, where the top drive was picked up. The bit was washed to 2998.0 mbrf (330.2 mbsf) before encountering any significant resistance. At that depth, the driller noted that he was meeting resistance (taking weight). The next 6 h was spent washing, reaming, and pumping multiple sepiolite mud sweeps to clean and condition the hole once again from 2998.0 mbrf to TD at 3018.0 mbrf. By 2000 h on 15 July, we were comfortable with the shape the hole was in. We then pulled the pipe back up into the 16 inch casing shoe and waited 1 h for the hole to equilibrate. No overpull or drag was encountered during the trip up to the casing shoe, which was a good sign. At 2130 h, we began lowering the pipe slowly to TD with minimal pump (30 spm) and no rotation. At TD, we swept the hole one final time with 50 bbl of sepiolite mud and pulled out of the hole. No significant resistance was encountered, and we felt certain that the last remaining vestiges of problem spots had been removed. By 0500 h on 16 July, the bit was on deck and we began making up the 10¾ inch casing string for the second time.

Second attempt at deploying 10¾ inch casing

The same casing string consisting of 29 joints of 10¾ inch (40.5 lb/ft; K-55; range 3) casing was made up, along with a cementing float shoe and the 10¾ inch casing hanger. The total string length was the same as that deployed during the first attempt (342.50 m). The DQ running tool was made up, and the casing was deployed via the drill string. The vibration-isolated television (VIT) camera was installed, and Hole U1301B was reentered for the sixth time at 1425 h on 16 July. The casing was run in hole to 2964.5 mbrf, and the top drive was picked up. Lowering continued to ~3005 m, where minor resistance was met. The casing was encouraged to move down another meter by increasing the pump stroke. The cementing manifold with a pre-made-up drill pipe single was made up and the cementing hose was connected.

This new technique worked well, and mud pump circulation was shut down for only 2 min, 55 s. With the manifold in the string, we resumed lowering casing and landed the casing hanger at 1615 h on 16 July. Proper latch engagement was verified with 15,000 lb of overpull. The 10¾ inch casing shoe was cemented at 346.1 mbsf with 32 bbl of 15.2–15.8 ppg cement. Heavier cement was pumped at the shoe. The cement was displaced with the rig mud pumps, the cementing dart was released, and the SSR plug was landed with 500 psi. The pressure was vented at the standpipe manifold, and a check for backflow proved negative. The casing running tool was released with 3¼ turns of right-hand rotation, and it was raised to 2657.0 mbrf. After flushing and laying out the cementing manifold, we set back the top drive and recovered the camera. Prior to retrieving the drill string, the drilling line was serviced (slip and cut). The pipe trip was completed while the ship moved to Hole 1026B. A positioning beacon (SN 2193; 14.0 kHz; 208 db) was deployed at 2356 h, and by 0045 h on 17 July, the casing running tool was detorqued and laid out, ending operations in Hole U1301B for now.

Transit to/from Site 1026

Before continuing further operations at Site U1301, we decided to move over to Hole 1026B to remove a mini-reentry cone installed in the top of the existing CORK. See "Operations" in the "Site 1026" chapter for a detailed description of these operations. We conducted the 1.08 km transit to and from Hole 1026B in DP mode while retrieving the drill string.

Return to Site U1301

Depth measurement check in Holes U1301A and U1301B

The first operation during this occupation of Hole U1301B was to drill out the 10¾ inch casing shoe, the SSR plug/dart assembly, and any remaining cement. A 9⅞ inch tricone drill bit was made up to a three-stand BHA and lowered to the seafloor.

Prior to reentry into Hole U1301A, we decided to conduct a thorough depth check in both Holes U1301A and U1301B. Using the drill string pipe tally and the camera system, we visually verified the seafloor depth, the depth for the top of the cuttings mound (at a single location), and the depth to the top rim of the installed reentry cones. By taking these measurements simultaneously over a 30 min period, we minimized tidal effects (Fig. F6), giving us accurate depth references for each hole as well as accurate comparison depths between holes. These data were important in accessing whether the final resting locations of the reentry cones were likely to present future ROV or submersible accessibility problems to the CORK head instrumentation bays. The results of these depth measurements are given in Tables T2 and T3. It was determined that both reentry cone rims were below the seafloor. Because of the buildup of cuttings above the top of the Hole U1301B reentry cone, the CORK to be installed in this hole would have to be raised 2.0 m prior to installation. Later in the expedition, we received a helicopter transfer with the required equipment to extend the height of the CORK head.

Hole U1301A

Drilling out 10¾ inch casing shoe

With the depth measurement exercise completed, Hole U1301A was reentered for the seventh time at 1940 h on 17 July 2004. The camera was recovered back on board ship while the pipe was lowered into the hole run and the top drive was picked up. The float shoe was drilled out in 45 min, and the bit was then lowered without rotation and without circulation to see how much unrestricted depth of hole was available. Tag depth was recorded at 2963.5 mbrf with 15,000 lb of weight set down. This equates to 296.2 mbsf, which is 34.0 m into basement or 19.1 m below the 10¾ inch casing shoe. The 9⅞ inch drilling assembly was retrieved, and at 0315 h on 18 July, the bit and bit sub were laid out and we began preparing for hydrologic (packer) testing.

Hydrologic (packer) testing

A packer testing BHA was assembled consisting of a clean-out bit, an 8¼ inch, 10 ft long drill collar pup, the TAM International packer assembly with a 5 ft element, eight 8¼ inch drill collars, and a TDC. This BHA was lowered and the camera/sonar system was deployed. Prior to reentry and offset from the reentry cone, a drill pipe wiper pig was pumped through the drill string to wipe out any rust or corrosion residue remaining; this was to ensure that any residue would not interfere with the hydrologic testing. Hole U1301A was reentered for the eighth time at 0901 h on 18 July. After recovering the camera, lowering pipe to 2941.0 mbrf, and picking up the top drive, the packer assembly was positioned inside the last (shoe) joint of 10¾ inch casing (2941.0 mbrf). A packer setting go-devil was deployed, and 1 h was spent recording a hydrostatic baseline pressure. At 1200 h on 18 July, the packer was inflated with 1000 psi pressure, and 10,000 lb of weight was set down on the packer to keep it from creeping uphole. Another 1 h was used standing by for a formation baseline pressure, and at 1300 h a series of constant-rate injection tests were conducted into the formation. Injection testing was completed at 2330 h, at which time the packer was deflated and the wireline was lowered to recover the packer go-devil. The drill string was retrieved back on the rig floor by 0730 h on 19 July.

Hole U1301A CORK installation

The final configuration of the CORK installed in Hole U1301A is shown in Figure F7.

After rigging up for running 4½ inch casing, three 6 m long "slotted" pup joints were made up with a casing bull plug on the bottom. The bull plug had a bar welded across the face to prevent any instruments from passing out the bottom of the 4½ inch casing string should the instrument string fail. The slots (cut with a plasma cutter) were put in the casing pups to allow free flow of formation fluids through the lower part of the instrumentation string. The landing sub was made up, along with a single 4½ inch casing packer. Three miniscreens were installed at the approximate center of the slotted casing joints (~10 m below the packer). Another four miniscreens were installed immediately below the packer. By 1200 h, the lower ends of the umbilical lines were connected. The umbilical for this installation was left over from Leg 196. The Hole U1301A CORK used 278 m of umbilical, and 234 m of the Leg 196 umbilical remains on the drum for possible future use. The next 8 h were spent making up 18 joints of 4½ inch casing and two 6 m long pup joints, strapping umbilical lines to the casing, installing casing centralizers (~2 per joint; 48 total), making up the CORK running tool to the CORK head assembly, connecting the packer inflation hose from the running tool to the head, and making up the remaining BHA required for the deployment. The BHA consisted of the CORK running tool, five 8¼ inch drill collars, a TDC, and the usual two stands of 5½ inch transition drill pipe.

The assembly was lowered into the moonpool, where a bent valve handle was replaced and a single osmotic sampler was attached. The moonpool doors were opened, and the large camera/sonar sleeve was test fitted over the CORK head to ensure that there would be no interference passing over it when the time came for the camera to be lowered down the end of the 4½ inch casing for reentry. At 2000 h on 19 July 2004, we began lowering the CORK assembly to the seafloor. The camera was deployed, and at 0045 h on 20 July, Hole U1301A was reentered for the ninth time. The casing was lowered until just before landing into the 10¾ inch casing, and the top drive was picked up.

CORK head identification

The CORK head deployed in Hole U1301A had a wide black stripe painted circumferentially near the top of the structure just below the lugs used for engaging the CORK running tool. In the middle of the large black stripe was a small white stripe.

Deployment of CORK osmotic sampler/thermistor string

At 0245 h, we began making up the internal OsmoSampler/thermistor instrument string. This consisted of a lower sinker bar, four osmotic samplers, a lower "gravity plug" seal sub, a section of ⅜ inch Spectra rope with two thermistors installed, another sinker bar, another section of Spectra rope, and an upper "gravity plug" seal sub. The assembly was deployed at the rig floor by using two sheaves, two tuggers, and a series of rope "grippers" that were systematically braided onto the Spectra rope and then removed prior to entry into the drill pipe. Once made up, the entire (~294 m long) assembly was lowered through the pipe and down inside the CORK using the core winch with a special sinker bar assembly consisting of three sets of wireline jars installed in series. A special "weakened" shear pin was installed in the overshot. Once landed in the CORK head, the instrument string was released by jarring and severing the shear pin. The sinker bar assembly was recovered, and a packer setting go-devil was dropped down the drill string. This go-devil was used in the past as a backup way of inflating the 4½ inch casing packer should the seals in the CORK running tool "stinger" fail to seal properly. At 0745 h, after activating the AHC, the CORK head was landed in the 10¾ inch casing hanger. The 4½ inch casing packer was inflated with 600 psi pump pressure, and this pressure was held for 30 min. The camera was recovered, and preparations began for deployment of the ROV/submersible platform.

Deployment of ROV/submersible platform

The ROV/submersible platform used in Hole U1301A was of the older design. It was made up of gray plate steel with holes cut in it to aid in the passage of water through the structure during deployment. This platform is distinctively different than the newer design deployed in Hole U1301B. The new platforms, although they are also gray in color, are made up of steel grating material and are not solid metal. One quadrant of the Hole U1301A platform was outlined with a black paint stripe to give the DP operators a directional orientation reference. On the surface of the platform there were two opposing black squares painted with white numbers "1301A."

The ROV/submersible platform was moved into the moonpool, and final assembly (bolting/welding) was completed. A newly designed mechanical platform deployment tool (see Fig. F7 in the "Site 1026" chapter) was made up to the platform, and the assembly was deployed on the logging line via the new Schlumberger heave-compensated logging winch. In the past, the platforms were deployed using the logging line and a wire rope bridle attached to an acoustic release. Once landed, the platform was released by lowering a portable transducer over the side of the ship and sending a release command sequence to the subsea release system. The new mechanical system is designed to release the platform automatically as the deployment tool encounters the top of the CORK running tool. At 1400 h on 20 July, the platform reached the CORK; however, the weight of the platform was not released. When the winch operator picked up, he had ~1300 lb of overpull. The cable was slacked off a second time, and once again the winch operator picked up. This time, with a few hundred pounds of overpull, the tool came free and the static hanging weight indicated that the platform had been released. Upon recovery, one of the three arms on the running tool had bent. Two arms released properly and the third apparently hung up momentarily, which was long enough to put that portion of the mechanism in a bind. In retrospect, we believe one of the arms was hammered into place during attachment to the platform, and this is likely the one that did not release cleanly. The platform deployment tool was repaired, and the next time it was used, more care was given to making sure that the three engagement arms were fitted to the platform with the necessary clearance for a less forceful release.

By 2400 h on 20 July, the platform deployment tool had been recovered and the camera was deployed to inspect the CORK installation. The installation appeared to be fine. The CORK running tool was quickly released, and the drill string was retrieved. The camera was recovered, and the coring line was deployed to recover the packer setting go-devil. To our surprise, the overshot contacted the packer setting go-devil at 1540 mbrf. Apparently, the go-devil never properly seated in the CORK running tool as it was supposed to. Although this was a backup mechanism, there was still some concern as to why the go-devil hung up in the drill string. After taking measurements of the go-devil body, we found that the upper diameter of the tool measured a larger diameter than the drill pipe drift used in "rabbiting" our drill pipe to ensure a clear bore. The investigation is continuing as to why this go-devil was designed the way it was. It was not used for other CORK deployments during Expedition 301.

During the pipe trip, the ship was moved 36 m back to Hole U1301B, and by 2400 h on 20 July, all tools had been recovered, ending operations for Hole U1301A.

Hole U1301B

Drilling out 10¾ inch casing shoe

A 9⅞ inch tricone bit and drilling BHA was assembled and lowered to the seafloor. After deploying the camera and spacing out the drill string, Hole U1301B was reentered for the seventh time at 0525 h on 21 July 2004. The pipe was lowered to bottom, the top drive was picked up, and the 10¾ inch casing shoe, SSR plug assembly, and remnant cement were drilled out. The rathole below the shoe appeared clean, and no fill was encountered. Once on bottom, we drilled another 1.0 m of new hole to provide some stabilization for the RCB core bit soon to follow. The hole was swept with 20 bbl of sepiolite mud, and the drilling assembly was recovered back on board ship by 1530 h on 21 July.

RCB coring in basement—first bit run

The Hole 1301B coring summary is shown in Table T1. A 9⅞ inch RCB (CC-7 style) coring bit was made up with a mechanical bit release (MBR) and the remaining subs associated with the RCB outer core barrel assembly. A six-stand BHA was made up and lowered to the seafloor. The unusual number of drill collars allowed us to reach an adequate depth (100–150 m) on the first RCB bit run without exposing the top of the TDC to open and possibly unstable hole. Prior to reentry, the drilling line was serviced (slip and cut), and at 2215 h on 21 July, Hole U1301B was reentered for the eighth time.

After picking up the top drive, continuous RCB coring commenced at 0300 h on 22 July. Coring continued with variable parameters. Hole instability seemed to be associated with those portions of the hole where rapid penetration rates (4–6 m/h) were encountered. Core recovery also decreased in these "brecciated" intervals, and the drilling torque became higher and erratic; however, we were able to clean up these problem sections of hole. In the more massive portions of basement, the ROP slowed down dramatically with progress in the 1.0–3.0 m/h range. The first bit run continued until 0300 h on 25 July, when Core 15R was recovered. This core was excellent, with 9.6 m advanced and 4.92 m of fairly massive core recovered (recovery = 51.3%). The ROP for Core 15R averaged 1.5 m/h, although major tidal influences (±2 m per day) continued to complicate our drilling depth references (see Fig. F6). Total depth achieved to this point was 3121.0 mbrf (453.2 mbsf). A total of 102.0 m was cored, with the first bit achieving a recovery of 31.41 m (30.8%) and requiring 53.0 total bit rotating hours. We decided to retrieve the bit at this time to be conservative and to help minimize chances of a bit failure that might junk the hole. Recovery probably could have been improved substantially by deploying barrels without core liners and by cutting half rather than full cores, but the scientists considered deep penetration to be of equal importance to good recovery.

A wiper trip was made back up to the 10¾ inch casing shoe and then back to TD, where ~7 m of fill was encountered. The fill easily washed away, and the hole was swept with another 30 bbl of sepiolite mud.

RCB coring in basement—second bit run

Consideration had been given earlier to running a C-4 core bit in lieu of another C-7 style. The C-4 has a slightly longer tungsten carbide insert and might have achieved a slightly faster rate of penetration. Once the initial bit was recovered, however, that idea was abandoned. Although the bearings were in excellent condition, the cutting structure was not. All buttons were broken on the ID gage cutters, and there were broken, chipped, or missing teeth on all other rows. The bit was considered junk. Because of the large number of broken teeth on the first bit, it was considered unwise to run a bit with longer teeth. Therefore, another new C-7 core bit was made up to a rebuilt MBR. Another three drill collars were picked up, enabling us to run a seven-stand BHA. This allowed us to core up to 186 m beyond the 10¾ inch casing shoe without exposing the smaller-diameter TDC to open hole. With the first bit advancing to 107.1 m beyond the shoe, the longer BHA would now allow us to core another 79 m. The pipe was lowered to bottom, and Hole U1301B was reentered for the ninth time.

While lowering the bit through the 10¾ inch casing, the driller noted that there was an obstruction inside the 10¾ inch casing at 2918.2 mbrf. Even setting down a weight of 30,000 lb, the bit would not pass this point. The top drive was picked up, and with only minimal rotation the bit passed through the spot with little problem. The driller picked up above the point and when he came down a second time, once again the interference was identified at exactly the same depth. We had not seen this phenomenon on either of our first two trips through the 10¾ inch casing string (later on we would find that this was the lower portion of the 10¾ inch casing that had backed off). Unable to do anything about the problem, we continued on to bottom washing and reaming from 3106.0 m to 3121.0 mbrf (TD). The hole was swept once more with 50 bbl of sepiolite mud, and the center bit was recovered.

At 0030 h on 26 July, we resumed RCB coring in basement. Coring proceeded well initially. Sepiolite mud sweeps (30 bbl) were pumped every connection. The hole appeared to be in good condition with no overpull or fill on bottom. Coring continued through Core 26R to 3186.8 mbrf (519.0 mbsf). When picking up off bottom after cutting Core 26R, the driller noted 40,000 lb of overpull and high torque off bottom. The hole was swept with 30 bbl of sepiolite, and the pipe was raised to 3157.0 mbrf before recovering Core 26R. Because the torque remained high, we elected to take time for hole cleaning and conditioning. We conducted a wiper trip up to the 10¾ inch casing shoe, noting overpulls of 50,000 and 30,000 lb at 3101.0 and 3073.0 mbrf, respectively. The hole was washed and reamed back to the bottom, where 12 m of soft fill was easily circulated out. Drilling torque returned to normal, and at 2230 h on 28 July, we resumed RCB coring. By 0630 h on 29 July, we had advanced the hole to 3200.0 mbrf (532.2 mbsf). The hole was swept with 30 bbl of sepiolite mud, Core 28R was recovered, and at 0815 h, we began to retrieve the bit for our second bit change. During the pipe trip, the driller worked the pipe several times through the earlier identified trouble spot at 2918.2 mbrf (inside the 10¾ inch casing). The driller repeatedly raised and lowered pipe from above 2918.0 and down to 2924.0 mbrf (which was simply a convenient drill pipe connection) without incident. There was no indication of any residual problem in that area (see later problems with backed off 10¾ inch casing). At 1530 h on 29 July, the bit was back on board and we began making preparations for making up the new coring BHA.

RCB coring in basement—third bit run

A new C-7 core bit was made up to another rebuilt MBR. An additional nine drill collars were picked up, enabling us to run a 10-stand BHA. This allowed us to advance the bit up to 268.5 m beyond the 10¾ inch casing shoe without exposing the smaller-diameter TDC to open hole. With the current total depth at 3200.0 mbrf, we were able to core ~83 m deeper with this third bit for a total of ~350 m into basement. The pipe was lowered to the seafloor, and Hole U1301B was reentered for the tenth time. While lowering pipe inside the casing, the driller noted an obstruction at 2926.0 mbrf. This was 8 m lower than the previous encounter. The top drive was picked up, and the camera was recovered. The pipe was rotated through the obstruction in the casing without difficulty. As before, the torque above and below that point was normal and consistent. The location of the trouble spot had moved down from 2918.2 on the last (second) bit trip to 2926.0 mbrf. We speculated (incorrectly) that the casing string was deflected because of an irregular and/or deviated hole and that the drill collars/drill pipe tool joints had been wearing a hole/slot (on low side) in the side of the casing at that depth. Later, we determined that the lower part of the 10¾ inch casing had backed off and dropped down. After running the rest of the way to bottom, the hole was swept with 50 bbl of sepiolite mud and RCB coring was initiated. Coring continued until Core 36R was on deck at 1400 h on 31 July. We terminated coring, as we achieved the primary objectives of obtaining substantial penetration deeply into extrusive basement and we felt it was wise to save extra time to deal with any uncertainties associated with the remainder of the expedition objectives (this turned out to be a wise decision).

Distress call

During the last few hours of coring in Hole U1301B, the ship's radio officer picked up a distress call communication between the U.S. Coast Guard (USCG) and a sailing vessel. The sail boat, with six people on board, was located ~31 nmi to the west of the JOIDES Resolution and was taking on water. We advised the USCG of our time to recover drill pipe and reach the location of the emergency. We also offered the use of our helideck and helicopter fuel if they were required for rescue operations. The USCG out of Port Angeles, Washington (USA), was handling the situation. We were not requested to cease operations, and later information indicated that the vessel was not in danger of sinking and that its pumps (hand pumps and buckets) were keeping up with the ingress of water. Apparently, a powered bilge pump was not operational and the source of the leak was also unknown at the time. Ultimately, the USCG dispatched a fixed wing "Buffalo" aircraft to the scene and air dropped a pump to the sailboat. The vessel continued to its home port of Seattle, Washington (USA).

Preparations for wireline logging

With the cutting of Core 36R, the final depth of Hole U1301B was established at 3250.6 mbrf (582.8 mbsf). This yielded an ultimate penetration below the basement contact of 317.6 m. A wiper trip was made up to the 10¾ inch casing shoe and back to TD. No problems were experienced with the wiper trip. Only 8 m of soft fill was identified on bottom, and this was easily circulated out with a 50 bbl sepiolite mud sweep. The bit was pulled back up into the 10¾ inch casing, and the earlier identified problem areas were checked by raising the bit past 2918.0 mbrf and lowering the bit down until it shouldered (took weight) at 2926.0 mbrf. As before, slight rotation with the top drive allowed the bit to pass and the string was free below this depth. The pipe trip out of the hole continued, and, once clear of the reentry cone, the ship was offset 20 m to the north. The shifting tool was lowered, and at 0130 h on 1 August, the bit was released from the drill string. The ship was positioned back over the hole, and at 0147 h, Hole U1301B was reentered for the eleventh time. The drill string was tripped to 2933.0 mbrf (265.2 mbsf), or slightly below the trouble spot inside the 10¾ inch casing. The top drive was once again used to rotate past this point. At 0415 h on 1 August, we began rigging up the logging sheaves for wireline logging.

Wireline logging

The Schlumberger logging sheaves were rigged up, and at 0415 h on 1 August, we began rigging up the first logging tool suite.

Triple combo

The first tool string included the Logging Equipment Head–Mud Temperature (LEH-MT), Hostile Environment Natural Gamma Ray Sonde (HNGS), Hostile Environment Litho-Density Sonde (HLDS), Accelerator Porosity Sonde (APS), and SlimXtreme Array Induction Tool (QAIT). The first pass with this tool string reached a total depth of 3246 mbrf. The second pass reached a total depth of 3122 mbrf. The caliper arms were fully extended during the first pass at 3242 mbrf.

Ultrasonic Borehole Imager

The second tool string included the LEH-MT, Scintillation Gamma Ray Tool (SGT), General Purpose Inclinometer Tool (GPIT), and Ultrasonic Borehole Imager (UBI). The second tool string deployment required slow deployment speeds because of low tool string weight. An obstruction was encountered in the hole at 3096 mbrf. There were two passes in open hole from ~3096 to 3021 mbrf before repositioning the open-ended pipe at 2914 mbrf. Two passes were made to log the casing interval from 3021 mbrf to seafloor. The UBI data were used to attempt to confirm the length of the gap between the two backed-off sections of 10¾ inch casing.

Formation MicroScanner-sonic

The third tool string included the LEH-MT, SGT, Dipole Sonic Imager (DSI), GPIT, and FMS. The third tool string deployment stopped at 2900 mbrf for recording uphole and downhole acceleration with the AHC on and off. An overpull of ~6000 lb was detected at ~3072 mbrf during the second pass. After the deployment, the logging engineer had to cut off 150 ft of Hi-T logging line and rehead the rope socket because of several kinks in the cable.

Vertical seismic profile

Even though the three-component Well Seismic Tool (WST-3) checked out several days prior to deployment, there were problems getting the tool to respond on deck prior to running in the hole. The backup single-channel WST was deployed instead. While running in the hole with this tool, the arms appeared to keep opening. The deployment took 2 h to reach the seafloor because of the tool's light weight. On several occasions, descent was stopped to close the arm. The initial deployment speed was ~1000 ft/h, and this increased to 7700 ft/h with depth. Based on caliper observations, three potential intervals were identified for WST stations. Clamping and data were recovered at depths of 3075, 3050, and 3025 mbrf. While pulling out of the hole, we slowed down to ~2500 ft/h to allow the rig floor crew to work on the AHC and then subsequently increased the speed to ~9000 ft/h. At the rig floor, we noticed that the clamping arms were fully extended, although they had been previously closed before entering the pipe. In support of the VSP program, the generator injector (GI) gun was used. The gun configuration consisted of a 45 inch³ generator volume, a 105 inch³ injector chamber volume, and a total pressure of 2000 psi. Data were recorded at 1 ms sampling interval, and the monitoring hydrophone was attached to the GI gun, which was placed 2 m below sea level. The delay time used for all shots was 40 ms, and the recording length was 5 s with a starting point at 600 ms.

At 1500 h on 2 August, the logging sheaves were rigged down and the wireline logging program in Hole U1301B was completed.

Transit from Hole U1301B to Hole 1026B for CORK replacement

After the drill string was recovered and fifteen 8¼ inch drill collars were laid out, we began the 1.08 km DP move to Site 1026 to install a CORK-II in Hole 1026B. For details of the CORK replacement in Hole 1026B, see "Operations" in the "Site 1026" chapter.

Transit from Hole 1026B to Hole U1301B

After finishing the Hole 1026B CORK-II installation (1130 h on 5 August 2004), we moved the ship back to Hole U1301B in DP mode while retrieving the CORK running tool. Once the running tool was secured on deck, the drilling line was serviced (slipped and cut).

Attempted remedial cementing of 10¾ inch casing gap

This reoccupation of Hole U1301B was to attempt remedial cementing of the 10¾ inch casing that had backed off while RCB coring. A custom cementing assembly was designed and fabricated on board the ship. This consisted of a "stabbing sub" fabricated from an old head sub with the square rotary connection shoulder machined to a 45° taper, two stands of 8¼ inch drill collars, an internally blanked-off head sub, a ported cementing sub fabricated from a 36 inch long 8¼ inch drill collar pup with three torch-cut 1¼ inch diameter holes, and two additional 8¼ inch drill collars. The remainder of the BHA was the typical TDC and two stands of 5½ inch drill pipe. The custom cementing assembly was lowered to the seafloor, and Hole U1301B was reentered for the twelfth time. The pipe was lowered to 2925.3 m, where the driller noted a weight decrease. Once again, this spot in the casing could not be passed without rotation. The top drive was picked up, and the pipe was rotated easily into the lower portion of the 10¾ inch casing string. It should be noted that, based upon an inspection of the MBR recently pulled out of the hole after logging, the 10¾ inch casing string most likely backed off at the casing coupling, leaving the coupling at the top of the lower section of casing looking uphole. Once past the open section of casing, the pipe was lowered to the perceived depth of the 10¾ inch casing shoe at 3019.0 mbrf. At that point, 15 bbl of high-viscosity bentonite gel mud was displaced into the hole. This was intended to help "float" the later displaced cement and keep it from falling downhole and out of the desired position. Bentonite gel mud was used for this so that we could keep freshwater- rather than seawater-based mud in the hole. Once the mud was displaced, the pipe was pulled back uphole and positioned so that the "ported sub" was located at ~2924 mbrf, or just a 1–2 m above the estimated depth of the backed-off casing coupling. A 6% mix of freshwater and bentonite gel mud was premixed and then mixed with class G cement to make up a 10 bbl, 15 ppg cement slurry. Once the bentonite-water combination was added to the cement, the mix became very thick and almost unpumpable. With the cementing units pumps straining, the slurry was eventually pumped into the pipe and displaced downhole with the rig pumps. The cement pill was preceded and followed by 10 bbl of fresh drill water to help isolate the cement slurry from the seawater. Once the cement was displaced into position in the hole, the drill string was pulled up again and the "ported sub" was repositioned at 2954.0 mbrf (the top of the calculated cement plug). A drill pipe cementing wiper dart was then pumped to bottom, stopping in the blanked-off sub located below the "ported sub." The drill string was then flushed thoroughly with seawater. The BHA was spaced out for this exercise so that while waiting for the cement to cure we could leave at least one stand of drill collars inside the lower section of 10¾ inch casing to try to keep it aligned with the upper portion of 10¾ inch casing above. While standing by waiting for the cement to harden, we circulated slowly at ~40 spm and rotated the pipe slowly at ~15–20 rpm. This was to ensure that we did not cement our BHA in the hole or at least could recognize if that began to happen. After waiting 7.75 h, we pulled pipe to 2900.0 mbrf and set back the top drive. The remainder of the drill string was then retrieved, and the BHA was back on the rig floor at 1700 h on 6 August, completing the attempted remedial cementing operation. We then decided to conduct APC coring in Hole U1301C to give the cement additional time to harden.

Hole U1301C

APC coring

The Hole 1031C coring summary is shown in Table T1. A typical three-stand APC/XCB coring BHA was made up, and the XCB/center bit and APC core barrels were spaced out. The APC core barrels to be used were dressed with liners and core catchers, and the drill string was lowered to 2652.1 mbrf, where the top drive was picked up and the pipe was spaced out for spudding. An APC core barrel was deployed via the core line, and with the bit positioned at 2663.0 mbrf, Hole U1301C was spudded at 0010 h on 7 August 2004. Core 1H recovered 5.08 m, establishing a seafloor depth of 2667.4 mbrf. We cored the sediment section in Hole U1301C to collect high-quality APC samples for geochemical and microbiological studies. We cored continuously from the seafloor to 119.1 mbsf (Cores 1H through 13H). After that, we alternately cored and drilled ahead without coring to ensure we had sufficient time to obtain samples from the deepest sediments. We penetrated a total of 265.3 m, cored 166.8 m, and recovered 143.29 m (86%). We pushed the APC coring system beyond its routine operational limits to obtain APC cores from the deepest sediments above basement. Cores 15H and 16H extended from 178.1 to 197.1 mbsf and recovered 11.87 m (62%). After drilling ahead to 235.8 mbsf, we took Cores 17H through 19H from 235.8 to 265.3 mbsf in the pelagic section just above basement. These cores recovered 24.19 m (85%) and terminated just decimeters above basement. The APC core barrels failed to achieve full stroke after Core 6H; however, good quality core samples were still obtained; we raised the bit ~1 m before shooting each core. The cores were heavily sampled for microbiological and geochemical studies on the catwalk. PFT was pumped continuously for all APC cores. Five temperature measurements were attempted (APC-temperature tool [APCT] and DVTP), but two of these yielded poor-quality data due to tool motion or because of being pushed into poorly consolidated formation sands. Upon completion of APC coring, a small cement plug was displaced at the base of the hole and the drill string was recovered back on board ship. By 1530 h on 8 August, the APC coring BHA was back on board and preparations began for drilling out the cement placed earlier in Hole U1301B.

Hole U1301B

Drilling out cement and checking open hole depth

After completing APC coring in Hole U1301C, we moved the ship in DP mode back to Hole U1301B. We planned to drill out the remedial cement displaced 2 days earlier. We hoped that our attempt to keep the cement in place across the 10¾ inch casing gap was successful. After lowering a tricone drill bit and drilling BHA to the seafloor, we reentered Hole U1301B for the thirteenth time at 2125 h on 8 August 2004. The bit was lowered without resistance until contacting the top of the lower section of 10¾ inch casing at the predictable depth of 2926.0 mbrf. The camera was recovered, and the top drive was used to rotate slowly through this location and into the top of the lower casing section. As before, the entry into the lower casing was relatively easy and the remainder of the trip to total depth did not require any rotation. At no time was any cement contacted inside the casing string, so the assumption was that our remedial cement went the same way as all the others—down the hole and into the formation. The pipe was advanced to 3175.0 mbrf, which was considered adequate as an open hole depth check because there were no plans to exceed this depth with the any part of the CORK installation. The hole was swept one final time with 30 bbl of sepiolite mud, the drill string was retrieved back on board at 0730 h on 9 August, and preparations for hydrologic (packer) testing began.

Hydrologic (packer) testing

The TAM packer BHA was assembled with a single packer element, and the surface circulation equipment was successfully pressure tested in preparation for packer slug and flow testing. The drill string was lowered to the seafloor, and Hole U1301B was reentered for the fourteenth time at 1310 h on 9 August. The pipe was advanced all the way to 3152.0 mbrf, placing the packer at the first set point of 3140.0 mbrf. No problems were experienced on the trip except for what has become the traditional rotation into the top of the lower 10¾ inch casing string at 2926.0 mbrf. The first packer tests were conducted from 1745 h on 9 August until 0215 h on 10 August. The packer was then deflated, and the pipe was raised to the second packer test depth of 3110.0 mbrf. This second set of packer tests was completed at 0700 h. The packer was again deflated, and the pipe was raised to the third packer test depth of 3085.0 mbrf. These packer tests were completed at 1200 h, the packer was deflated, and the pipe was raised for a fourth and final time to the last packer set depth of 3047.0 mbrf. The last packer set was to check for a good packer seat only, and no flow testing was conducted at this depth. By 1400 h on 10 August, all packer work was completed and the packer go-devil was recovered. The top drive was set back and the pipe was recovered, clearing the seafloor at 1645 h. By 2100 h, all packer components were laid out on the rig floor. The packer element, after four successful inflation cycles, appeared to be in surprisingly good condition. The element had a few minor cuts and abrasions, and there was a slight memory (set) to the elastomer; however, there was no major damage identified. Based on the data recovered with the downhole digital gauges, all packer tests appeared to be successful.

Deployment of CORK "test" casing string

We decided that before assembling the entire CORK casing string, dual umbilicals, three packers, and head, we should run a test to ensure that the casing and bowspring centralizers could be coaxed across the gap in the 10¾ inch casing and into the lower section. At 2100 h on 10 August, we began rigging up the 4½ inch casing running tools. The first order of business was to determine how much weight was required to compress the bowsprings on our new 4½ inch bowspring centralizers. A centralizer was test-fitted inside our remaining 10¾ inch casing hanger with attached 10¾ inch casing pup joint by making up a centralizer to a single joint of 4½ inch casing. This was lowered into the hanger/pup assembly, which was secured at the center of the rotary table. The test was completed quickly, as the centralizer slid effortlessly into the casing, requiring only the weight of the 4½ inch casing joint. The 10¾ inch casing hanger was laid out, and assembly of the remaining 4½ inch test casing string began. The test string consisted of a 4½ inch casing bull nose, two joints of 4½ inch casing (slick), one joint of 4½ inch casing with two bowspring centralizers installed 5 m apart (to emulate having a casing packer in between), two more joints of 4½ inch casing (slick), a single 4½ inch casing joint and 2 m long casing pup with spring centralizer installed over the connection, a crossover from the 4½ inch casing eight-round thread (short) to a 5½ internal flush (IF) thread, and a standard crossover sub from the 5½ IF thread to the 5½ full hole thread on the 5 inch drill pipe. The casing crossover was fabricated by boring out a retired saver sub to accept a 4½ inch casing coupling and welding it inside and out. Welding was conducted with a pup joint installed in the coupling so as not to warp the coupling out of round. Once made up, the test string was lowered on the end of 5 inch drill pipe. The 5 inch pipe was used so as to more closely emulate the characteristics of the 4½ inch casing string to be deployed with the real CORK assembly. Hole U1301B was reentered for the fifteenth time at 0435 h on 11 August. The test string was lowered to 2888 mbrf, and the top drive was picked up. The string was then lowered to 2926 mbrf, where several attempts were made to pass into the lower section of separated 10¾ inch casing. No progress was made using only up and down motion of the string. The top drive was then rotated very slowly, and the string was worked up and down. It was interesting that the top drive would stall out without any WOB registering. Only very low torque was allowed to build up for fear of overtorquing the relatively weak eight-round casing connections. Once into the lower section of 10¾ inch casing, the end of the test string was advanced to 3002 mbrf, placing the 4½ inch casing test string and drill pipe crossover fully into the lower 10½ inch casing. The test string was then pulled back through the trouble zone and pulled back up to the surface. The seafloor was cleared at 0840 h, and by 1315 h on 11 August, the casing test string was rigged down and the drill crew serviced the drill line (slip and cut).

Initial deployment of CORK assembly

Deployment of the Hole U1301B CORK assembly was the most complex and arduous of the expedition. The CORK assembly consisted of a 4½ inch casing bull plug with a 4 inch ID, two joints of slotted 4½ inch casing (slick) with Teflon shrink tubing installed over 30 ft of casing and couplings, one 4½ inch casing packer (number 1) with three miniscreens installed directly below, two bowspring centralizers installed below the packer and one bowspring stabilizer installed above the packer, a gravity plug landing sub, two joints of 4½ inch casing, one 4½ inch casing packer (number 2) with three bowspring centralizers installed as on packer number 1, four joints of 4½ inch casing, one 4½ inch casing packer (number 3) with bowspring stabilizers installed as on packers number 1 and number 2, 32 joints of 4½ inch casing, and the CORK head. Note that 28 bowspring centralizers were installed over the first 215 m (18 joints) of 4½ inch casing. Teflon stabilizers (three each) were used on the nineteenth and twentieth casing joints. A total of 44 fixed stabilizers were used on casing joints numbers 21–40 to 470.6 m. A special new umbilical was deployed along with a special fabricated microbiology hose. In addition, the CORK running tool was modified with a special lockout (shear pin) ring that requires 4000–6000 lb of down force before the J-tool will function and release. The numerous packers, complex umbilical, and microbiology hose connections, the special bowspring centralizers, the centralizer locking rings, the welding of the centralizers to prevent rotation, and the 40 joints of 4½ inch casing led to an overall CORK assembly time of 22.25 h and required the assistance of numerous technicians and crew members; it took nearly three times longer than anticipated. At 1330 h on 12 August, we began lowering the CORK assembly, and Hole U1301B was reentered for the sixteenth time at 1630 h on 12 August. We then carefully lowered the assembly into the hole. The camera system was left down until the first packer was safely through the level of the reentry cone's throat. It was then pulled up above the CORK head so as to not risk losing the camera system should a failure occur in the casing string being deployed (as ended up happening). As we continued to lower the CORK, it appeared that the CORK casing, bull nose, casing packers, and bowspring centralizers passed easily through the gap in the 10¾ inch casing without incident. No rotation of the pipe was required. After picking up the top drive an additional joint of drill pipe was added to the drill string, placing the end of the CORK casing string at 3157 mbrf. This was ~12 m short of landing the CORK wellhead.

Open hole depth check with wireline sinker bar assembly

Because the OsmoSampler/thermistor string was destined to be deployed beyond the 4½ inch casing shoe (bull nose) into open hole, we decided to conduct an open hole depth check using a wireline sinker bar (2.125 inch outer diameter) string. The sinker bars were rigged up and lowered into the pipe at 2015 h on 12 August for this routine depth check. To our surprise, the sinker bars would not pass 2665 mbrf (seafloor at ~2667 mbrf). After repeated attempts to lower the wireline past this point, we decided to lower the camera system back down over the CORK head to assess the situation. Once the seafloor and reentry cone came into view, we were greeted by a horrifying sight. A good portion of the 4½ inch casing, umbilical, and so on, was piled up around the reentry cone; one end of the 4½ inch casing string with attached umbilicals could be seen extending from the throat of the reentry cone and draping over the outside edge. Another end of casing could be seen sticking up out of the seafloor sediment adjacent to the reentry cone. It was immediately apparent that one or more casing failures had occurred, leaving more than half of the deployed casing strewn about on the seafloor. With nothing else to be gained we retrieved the camera system and drill string. The CORK head was recovered with nothing attached to the lower end, and by 0600 h on 13 August it was laid out. One of the casing failures had occurred right at the coupling to the head itself. A portion of the pin thread from the last joint of 4½ inch casing was broken off inside the coupling and was recovered with the head. After review, it became apparent that this particular failure was because of excessive bending.

Seafloor inspection of reentry cone and seafloor

A short inspection BHA made up of a reentry cleanout bit and the transition stand of drill collars (two 8¼ inch drill collars and one TDC) was made up and lowered to the seafloor along with the camera system. At 1015 h on 13 August, we began to survey the aftermath of the 4½ inch casing failure(s). One joint of 4½ inch casing with umbilicals still attached was observed extending out of the reentry cone throat and was draped over the edge of the cone. We followed this section out ~30 m from the reentry cone until we identified what appeared to be the end. Another joint with a visibly identifiable plastic (polyethylene) centralizer was seen lying directly adjacent and tangential to the outside edge of the reentry cone. Yet another joint of 4½ inch casing was observed sticking up out of the seafloor in close proximity to the Hole U1301A reentry cone. As part of our survey, we moved 36 m back over to Hole U1301A and assured ourselves that the Hole U1301A CORK was still all right. Our best analysis of the failure at this time is that a bowspring stabilizer either hung up momentarily in the throat of the reentry cone/casing hanger area or a buildup of friction from the multiple bowspring stabilizers deployed caused the 4½ inch casing to buckle above the seafloor. This led to the failure of one or more 4½ inch casing connections. The umbilical still appeared to be attached and acted as a tension member holding many, if not all, of the joints together. We confirmed that the end of the 4½ inch casing string had not yet reached the gap in the 10¾ inch casing string, so that was ruled out as a possible cause. Our review of the rig instrumentation data remains inconclusive, and we have not yet been able to determine at what point in time the failure occurred, nor have we identified why we were not able to see the weight loss (~15,000 lb) that should have been associated with the failure. One explanation may be that the joints failed sequentially, and only small increments of weight were lost at a time. With the driller adding a stand of drill pipe at the same time, the gradual weight loss may have been partially masked. Analysis of the 1 s rig instrumentation data is ongoing, but it is clear that future CORK casing strings should be sufficiently weighted at the bottom to pull the casing into the hole. After satisfying ourselves that we had seen enough, we began to recover the seafloor survey BHA and simultaneously designed/fabricated a wall-hook-style fishing tool to be used in an attempt to drag the 4½ inch casing, umbilicals, packers, and so on out of the hole.

Fishing 4½ inch casing string

A wall-hook-style fishing tool was fabricated from 1¼ inch steel plate (Fig. F8) and welded to the same "jetting" sub used in fishing the aluminum reentry funnel in Hole 1026B earlier in the expedition. The new "rig-fabricated" fishing tool was made up to the transition string of drill collars (two 8¼ inch drill collars and one TDC). We tested how it would work on a 4½ casing pup joint on the rig floor. The fishing assembly was lowered to the seafloor. This time, the top drive was not picked up so that once the fish was engaged the driller would not have to lower the pipe to remove the top drive. Instead, torque to engage the casing body was provided by roughnecks using rig floor chain tongs. The first few attempts to engage the casing were unsuccessful when the driller could not get the hook underneath the bow in the casing. Ultimately, the casing was engaged at a spot just outside of the reentry cone rim. The entire time to hook the fish was <30 min. Estimates of the length of casing inside the reentry cone/casing varied from 200 to 250 m, so the drill pipe was raised to >300 m above the seafloor. The ship was then offset 300 m west of Holes U1301A and U1301B. The pipe was lowered back to the seafloor, and another 30 min and 300 A of top drive torque were required to release the fishing tool from the casing string. Large amounts of casing and umbilical and a casing packer were identified piled up on the seafloor. The entire release operation required ~30 min. With the fish gone, the ship was moved back over the Hole U1301B coordinates and we were pleased to see that only a single joint of 4½ inch casing was sticking out of the seafloor adjacent to the reentry cone. Apparently, nearly the entire CORK string was dragged 300 m to the west of the operating area. The reentry cone appeared free of any obstacles. Satisfied that we had accomplished our goal, the pipe was retrieved along with the fishing BHA and the camera, and by 0600 h on 14 August, the fishing assembly was laid out.

Open hole depth check

A used 9⅞ tricone drill bit was made up to a three-stand BHA and lowered to the seafloor, and Hole U1301B was reentered for the eighteenth time at 1030 h on 14 August. The pipe was lowered into the hole without any difficulty until reaching 2926 mbrf. Once again, the top drive had to be picked up to rotate the pipe slightly and the bit dropped through into the lower section of 10¾ inch casing. Once through the casing gap, the pipe was lowered without rotation or circulation, and 3245 mbrf was achieved by 1300 h without resistance. Total depth of the hole was 3250 mbrf; however, we stopped just shy of that depth to save the time of having to make up another stand of drill collars. A depth of 3245 mbrf was a more than adequate open hole depth check, as this depth was well below anything that would be deployed as part of the CORK installation. The bit was retrieved and back on board at 1800 h on 14 August. Preparations then began for the second deployment attempt of the U1301B CORK assembly.

Assembly of second Hole U1301B CORK

To avoid the problem that caused our first attempted CORK installation to fail, we elected to add a significant amount of weight to the bottom of the 4½ inch casing string. This would be analogous to the BHA or drill collars that are run at the end of the drill string to keep from putting the drill pipe into compression. Compression, or "buckling," is what led to the failure of the 4½ inch casing string during the first deployment in Hole U1301B. The CORK string had not been heavy enough for the driller to be able to tell if the string was going downhole or was hung up somewhere and the casing was buckling instead. The CORK for Hole U1301B consisted of the following: 4½ inch bull nose welded to the end of a stub of 5 inch drill pipe (1.97 m long), crossover sub, one 8¼ inch drill collar (with zip lift groove), two 3.05 m long 8¼ inch drill collar pup joints, one 4.58 m long × 8¼ inch drill collar pup joint (with zip lift groove), one 8¼ inch drill collar, two crossover subs, and one rig-fabricated crossover sub. The zip lift drill collars and two 3 m long drill collar pup joints were junk recovered with the Hole 1026B CORK and were drifted prior to use. This 32.5 m long CORK BHA added more than 10,000 lb of weight to the end of the 4½ inch casing string and provided a much-needed aid to the driller while deploying the CORK. With the CORK BHA assembled, we began making up the CORK casing string. The first casing packer was made up to the rig-fabricated crossover sub at the top of the CORK BHA. This was followed by the landing sub (for the lower gravity plug) and the first joint of 4½ inch casing. This allowed us to lower the casing packer into the moonpool area, where four miniscreens were installed below the packer, and these were protected by installing a bowspring centralizer. The Expedition 301 umbilical and the microbiology hose (Tefzel) were then both attached to the top of the first casing packer. The umbilical and hose were run simultaneously off their respective reels by using a wheel sheave for the hose and a banana sheave for the umbilical. Both sheaves were hung from the support beams directly below the rig floor rotary table. The next step was to make up two additional joints of 4½ inch casing followed by the second casing packer. Another four miniscreens were installed below the second casing packer, and after making up the microbiology hose and umbilical connections, we attached our final bowspring centralizer. This was once again installed directly below the packer to help protect the miniscreens and to provide a smooth transition and guide for the 8 inch diameter packer element. Another 31 joints of 4½ inch casing were assembled while the umbilical and microbiology hose were deployed along side. The umbilical and hose were made fast to the casing by stainless steel banding placed approximately every 2 m. This was also the case for the casing joints installed below and between the casing packers. Once the 4½ inch casing had been run, we changed out the elevator bales and picked up the CORK-II wellhead for Hole U1301B. The running tool was engaged by sliding it horizontally onto the CORK head while the latter was restrained within the confines of the pipe stabber. The end of the CORK head was prevented from moving by holding it with the pipe racker skate. The CORK wellhead/running tool assembly was picked up vertically with the drawworks, and we began to make up the lower connection to the top joint of 4½ inch casing. It was here that we realized that during the previous aborted deployment the lower end of the CORK body (made from 4½ inch casing) was slightly bent. This caused the head to wobble during make up and made it extremely difficult to make up the fine eight-round casing thread without cross threading. After several attempts, the thread was made up tight, and the connection was welded out top and bottom for added insurance. At this point, the master bushings were pulled from the rotary table and the CORK wellhead was lowered into the moonpool area, where the final umbilical and microbiology hose connections were made up. A stand of drill collars was made up to the top of the CORK running tool, and we then test-drifted the osmotic sampler sinker bar through the assembly to ensure that the bend in the CORK body would not interfere with the deployment of the instrument string later. Multiple packer inflation hoses were installed from the CORK running tool to the top of the CORK wellhead, and three osmotic samplers were installed on the CORK head. During installation of the samplers, a final plumbing inspection was conducted and it was noticed that one piece of tubing had been cut too short and had pulled away from the fitting. Approximately 1.25 h was required to cut a new piece of tubing and complete the plumbing. This included picking up the CORK head so all others could be checked. All were judged to be all right, and we began to deploy the CORK assembly at 1430 h on 15 August.

Deployment of CORK (second attempt)

The drill string and camera were lowered to the seafloor, and at 1745 h on 15 August, Hole U1301B was reentered for the nineteenth time. The CORK was lowered to 2926 mbrf, where the bottom of the 10¾ inch casing gap was tagged at the usual depth. The string was picked back up approximately one single (~9.5 m), and the AHC was engaged. At the rig floor, the pipe was marked off in four quadrants so that we could keep track of its rotational orientation. The string was then lowered a second time, once again tagging the top of the casing coupling. The pipe was raised and lowered twice. Each time the pipe was rotated ¼ turn using chain tongs. On the third attempt, the nose of the CORK BHA slipped inside the lower backed-off 10¾ inch casing and the driller quickly continued to lower away to prevent pulling the pipe out on an up heave. This marked the first time that we had been able to pass into the lower casing section without having to use the top drive at ~50 rpm. Use of top drive rotation at any speed would have been extremely risky during the CORK deployment because it would have been quite easy to inadvertently unlatch the running tool and drop the entire assembly prematurely. In case we did have to use some top drive rotation, a special modification to the running tool was made. This consisted of a shear ring that would lock the tool and prevent rotation until at least 6000 lb of download was applied. Although we felt this would help to mitigate some of the risk involved with using the top drive, we were all very much relieved that we were able to cross the casing gap without using the top drive. The next anxious moment was when the first casing packer crossed the gap. Although we felt reasonably confident that the bowspring centralizers installed below each casing packer would guide the packers into the lower casing, we were still a bit apprehensive. These feelings soon passed when both casing packers crossed the gap without difficulty. The CORK string was advanced to 3165 mbrf, which was within 11.8 m of landing the CORK head, and at 2230 h on 15 August, we paused to run an open hole wireline depth check in preparation for deploying the thermistor/osmotic sampler instrument string.

Deployment of CORK instrument string

A sinker bar string was lowered through the CORK slowly at ~25 m/min so as not to inadvertently inflate the casing packers. The casing packers have check valves at the top that are set at a cracking pressure of 350 psi. Any pressure over this amount could have initiated packer inflation. The open hole depth check was terminated at 3200 mbrf, which was well below the depth to which the CORK instrument string was to be deployed. The sinker bars were recovered, and at 0230 h on 16 August, we began assembling the Hole U1301B instrument string. This string was longer than the others deployed earlier in the expedition in Holes U1301A and 1026B. The same technique was used as was described for those earlier holes; however, it took a little longer. By 0545 h, we had completed the assembly and began deploying the instrument string using the core line. This time, a speed of 20 m/min was used so as not to float the lightweight Spectra (Tefzel) line or low-weight (60 lb) sinker bar. At 0845 h, we reached what we thought was the landing point. After multiple attempts at jarring off, we decided we had better recover the instrument string and inspect the Spectra rope. It was feared that the lightweight (neutrally buoyant) line could get underneath the upper gravity plug during the jarring operation and either become cut or prevent proper seating of the plug. The instrument string was brought back to the ship, and a thorough inspection indicated that everything was all right. A longer piece of hose was put around the Spectra rope at the very top to stiffen the line and prevent the ability of the line to double back on itself. An inspection of the "weak" shear pin in the overshot assembly found that the pin had sheared through one shear plane; however, the other shear plane (the pin is in double shear) had tried to shear through the thicker portion of the pin rather than the weakened portion. It was determined that this occurred because the pin was not centered properly when installed in the overshot. The shear pins were replaced and the instrument string was deployed again. The gravity plugs were landed and the overshot was sheared off at 1415 h. By 1545 h, the wireline was out of the hole and preparations began for advancing the CORK wellhead the remaining 11.8 m to the landing seat.

Final landing of CORK

With the AHC engaged, the Hole U1301B CORK head was advanced the final distance and landed at 1600 h on 16 August. The final 11.8 m of advancement was carefully made. Several times the CORK acted as though it was setting down against a ledge, and each time the weight dropped off and the string began to advance again. A few minutes were taken to study the camera image and assure ourselves that the wellhead was resting in the proper location. We then pressured up the drill string to 1000 psi and proceeded to inflate the two casing packers. This process was expected to take a while because the packer penetrations were only single ⅜ inch lines. While retrieving the camera system, we maintained the 1000 psi pressure on the system to ensure that we had full expansion of the packers. With the CORK landed, the middle of each packer was located at 3140.0 mbrf (472.2 mbsf), or 207.0 m into basement, and 3096.8 mbrf (429.0 mbsf), or 163.8 m into basement, respectively (Fig. F9). We bled off the pressure to the packers at 1700 h, and at 1715 h on 16 August, we prepared to deploy the ROV platform.

Deployment of Hole U1301B ROV platform

The ROV platform was modified for this installation to allow for reentry and displacing cement into the reentry cone (Fig. F10). Spotting cement into the reentry cone was intended to hopefully seal off the throat of the cone in the vicinity of the stacked casing hangers. This was deemed necessary because of our inability to install the 16 inch to 10¾ inch casing hanger seal (due to a design flaw) and because the separated and uncemented 10¾ inch casing allowed connectivity to the seafloor. This negated the hydraulic seal required for the long-term studies. The platform was also deployed differently in this hole. For the first time ever, the mechanical delivery system affectionately known as "Lula" (because of its resemblance to a lunar lander) was rigged below the camera frame. This negated the need to use the logging line and saved numerous hours in rigging. It took 30 min to attach Lula to the CORK platform and another 30 min to rig the VIT sleeve to Lula. The platform was lowered through the moonpool and lowered at a winch speed of ~30 m/min. The platform appeared to be rock stable during the deployment, and a picture-perfect simultaneous release of the three arms was witnessed in real time using the camera. By 2130 h, we had recovered and rigged down Lula, and we ran the camera back to bottom to review the installation and unlatch the CORK running tool. Lula had to be recovered before this operation because of the slings used in rigging the deployment tool to the VIT sleeve. There was too much danger of snagging something on the CORK head if we tried to lower down far enough to adequately observe the unlatching process. By 2230 h, the camera was back down at the seafloor and we inspected the third and final successful CORK installation for Expedition 301. The running tool shear ring was not noticeable, and the unlatching process proceeded without incident. Prior to recovering the drill string, a few minutes were taken to get a good look at the top of the 4½ inch casing joint that was protruding out of the seabed directly adjacent to the Hole U1301B reentry cone. This was considered a potential hazard to future ROV or submersible operations, and we planned to fish this pipe out and deposit it at the same place as the rest of the casing string ~300 m west of Hole U1301B. The casing appeared to have a coupling facing up, and this provided us with the information we needed to build the appropriate fishing tool (Fig. F11). The drill string was then tripped back to the surface, where the CORK running tool was removed.

Cementing CORK head inside reentry cone

At 0415 h on 17 August, a cementing diverter pipe was made up to the end of the drill string transition pipe. It was lowered into the opening in the Hole U1301B CORK-II ROV platform (Fig. F10) at 0900 h on 17 August. This was the twentieth and final reentry of Hole U1301B. Fifteen barrels of high-viscosity bentonite gel mud was displaced into the reentry cone, and this was followed immediately with 9 bbl of cement. This was the last of the cement that we had on board. The drill string was pulled out of the ROV platform, and a drill string wiper dart was pumped down the drill string. The pipe was thoroughly flushed, and by 1430 h on 17 August, the drill string was back and the cement diverter tool had been laid out.

Fishing 4½ inch casing joint

A rig-fabricated fishing tool was fashioned (Fig. F11) from the hook tool used earlier to remove the aluminum reentry funnel from the top of the Hole 1026B CORK. A smaller insert was welded in to allow us to catch the coupling on the top of the 4½ inch casing joint. After making up the fishing tool, the pipe was run back to bottom and within 30 min the fishing tool was engaged on the fish and the casing joint was pulled out of the seafloor. The ship was offset 300 m west, and the joint was deposited on the seafloor with the other failed 4½ inch casing.

ROV/submersible hazard survey surrounding Holes U1301A and U1301B

With the fishing operation successfully concluded, we conducted a hazard survey with the camera system to identify any potential hazards that might pose a risk to future ROV or submersible operations at the site. A 100 m × 100 m area was searched, along with two 200 m long approach paths from the north and the east. At 2300 h on 17 August 2004, the survey was completed, and by 0415 h on 18 August, the drill string had been recovered back on board ship. While recovering the drill string, the ship was offset 20 m east of Hole U1301C to take the final cores of Expedition 301.

Hole U1301D

Hole U1301D was APC cored to recover sediment from an interval that had not been cored in Hole U1301C. We offset the ship 20 m to the east of Hole U1301C, lowered an APC/XCB BHA to the seafloor, and started drilling ahead at 1600 h on 18 August 2004. We drilled without coring from the seafloor to 120.0 mbsf using an XCB center bit. Cores 1H through 6H were taken from 120.0 to 177.0 mbsf and recovered 42.12 m (74%). PFT was pumped during all of the coring operations. We stopped coring once the depth objective was reached. The bit was retrieved and back on board at 0600 h on 19 August, and we began securing the ship for the transit to Astoria, Oregon.

Transit from Hole U1301D to Astoria, Oregon

The transit to Astoria began at 0900 h on 19 August 2004. The ship arrived at the pilot station outside the Columbia River bar at 0400 h on 19 August. Expedition 301 ended in Astoria, Oregon, with the first line ashore at 0700 h on 20 August.

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